Process for hydrocracking into a stage of hydrocarbon feedstocks

ABSTRACT

This invention relates to an improved process for hydrocracking into a stage of hydrocarbon feedstocks, using in a first reaction zone a pretreatment catalyst that exhibits a low acidity according to a standard activity test and an amorphous acid catalyst for hydrocracking that is free of zeolite in a second reaction zone that is located downstream from the first.  
     The objective of the process is essentially the production of middle distillates, i.e., fractions with an initial boiling point of at least 150° C. and a final boiling point that goes just up to the initial boiling point of the residue, for example less than 340° C., or else 370° C. and optionally oil bases.

[0001] This invention relates to a so-called improved process forhydrocracking into a stage of hydrocarbon feedstocks, comprising a firststage that is carried out in a first reaction zone with a hydrotreatmentcatalyst that exhibits a low acidity according to a standard activitytest and a last stage that is carried out in a second reaction zone thatis downstream from the first, with an amorphous acid catalyst forhydrocracking that is free of zeolite.

[0002] The objective of the process is essentially the production ofmiddle distillates, i.e., fractions with an initial boiling point of atleast 150° C. and a final boiling point that goes just up to the initialboiling point of the residue, for example less than 340° C. or else 370°C. and optionally oil bases (residue).

[0003] Prior Art

[0004] The hydrocracking of heavy petroleum fractions is a veryimportant refining process that makes it possible to produce, fromexcess heavy feedstocks that cannot be readily upgraded, lighterfractions such as gasolines, jet fuels and light gas oils that therefiner seeks to adapt his production to the structure of the demand.Some hydrocracking processes make it possible also to obtain a stronglypurified residue that can provide excellent bases for oils. Relative tothe catalytic cracking, the advantage of catalytic hydrocracking is toprovide middle distillates, jet fuels and gas oils, of very goodquality. Conversely, the gasoline that is produced exhibits an octanenumber that is much lower than the one that is obtained from thecatalytic cracking.

[0005] Hydrocracking is a process that draws its flexibility from threemain elements that are the operating conditions that are used, the typesof catalysts that are used, and the fact that the hydrocracking ofhydrocarbon feedstocks can be carried out in one or more stages.

[0006] The catalysts that are used in hydrocracking are all of thebifunctional type that combines an acid function with a hydrogenatingfunction. The acid function is provided by large-surface substrates (150to 800 m².g⁻¹ generally) that exhibit a superficial acidity, such ashalogenated aluminas (chlorinated or fluorinated in particular),combinations of boron oxides and aluminum oxides, amorphoussilica-aluminas and zeolites. The hydrogenating function is providedeither by one or more metals of group VIII of the periodic table, suchas iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridiumand platinum, or by a combination of at least one metal of group VIB ofthe periodic table such as molybdenum and tungsten and at least onemetal of group VIII.

[0007] The equilibrium between the acid and hydrogenating functions is abasic parameter that governs the activity and the selectivity of thecatalyst. A weak acid function and a strong hydrogenating functionprovide low-activity catalysts that work at a generally high temperature(greater than or equal to 390° C.) and at a low feed volumetric flowrate (the VVH that is expressed by volume of feedstock to be treated perunit of volume of catalyst and per hour is generally less than or equalto 2) but equipped with a very good selectivity of middle distillates.Conversely, a strong acid function and a weak hydrogenating functionprovide active catalysts that exhibit less advantageous selectivities ofmiddle distillates. The search for a suitable catalyst will therefore becentered on a judicious selection of each of the functions to adjust theactivity/selectivity pair of the catalyst.

[0008] Thus, one of the great advantages of hydrocracking is to exhibita great flexibility at various levels: flexibility at the level of thecatalysts that are used that provides a flexibility of feedstocks to betreated and at the level of the products that are obtained. An easyparameter to control is the acidity of the substrate of the catalyst.

[0009] The conventional hydrocracking catalysts can use weakly acidicsubstrates, such as amorphous silica-aluminas, for example. Thesesystems are more particularly used to produce middle distillates of verygood quality and also, when their acidity is very low, oil bases.

[0010] In the sparingly acidic substrates, the family of amorphoussilica-aluminas is found. A portion of the catalysts of thehydrocracking market are based on amorphous silica-alumina that iscombined either with a metal from group VIII or, preferably when thecontents of organic compounds that contain sulfur and nitrogen of thefeedstock to be treated exceed 0.5% by weight, with a combination ofmetal sulfides from groups VIB and VIII. These systems have a very goodselectivity of middle distillates, and the products that are formed areof good quality. These catalysts, for the less acidic among them, canalso produce lubricating bases. The drawback of all of these catalyticsystems based on an amorphous substrate is, as has been said, their lowactivity.

[0011] The catalysts that comprise a zeolite, for example anFAU-structural-type Y zeolite, exhibit a catalytic activity that ishigher than that of the amorphous silica-aluminas, but exhibitselectivities of light products that are higher.

[0012] In the processes where the hydrocracking catalyst is zeolitic, itis necessary to pretreat the feedstock on a hydrotreatment catalyst toeliminate the organic nitrogen that inhibits the activity of thezeolite.

[0013] On the other hand, the amorphous hydrocracking catalysts (withouta zeolite) readily support the presence of organic nitrogen andconsequently prior hydrotreatment to remove the heteroatoms is not used.Thus, these so-called “one stage” processes of the prior art do notcomprise hydrotreatment upstream from the hydrocracking since thehydrotreatment takes place on the hydrocracking catalyst.

[0014] However, the research work carried out by the applicant led himto discover that, surprisingly enough, in a process of hydrocrackinginto a stage that uses an amorphous hydrocracking catalyst, a conversionof the hydrocarbon feedstock, a selectivity of middle distillates(kerosene+gas oil) and a cycle time, higher than with the processes in aknown stage in the prior art, can be obtained provided that a reactionzone that comprises a hydrorefining catalyst that exhibits a low acidityis introduced upstream from the amorphous hydrocracking catalyst. Theaddition of this volume of hydrorefining catalyst is carried out withoutincreasing the overall catalytic volume nor reducing the flow rate ofthe feedstock that is to be treated. Therefore, the improvements thatare described above are obtained at a constant feed volumetric flow rate(VVH expressed by volume of feedstock to be treated per unit of volumeof the catalyst and per hour) relative to the processes of the prior artusing only an acidic amorphous catalyst for hydrocracking.

Detailed Description of the Invention

[0015] The invention describes a process of hydrocracking, hydrocarbonfeedstocks (for example called process “in one stage”) for theproduction of middle distillates and optionally oil bases that compriseat least a first reaction zone that includes hydrorefining, and at leasta second reaction zone , in which the hydrocracking of the effluent thatis obtained from the first reaction zone is carried out.

[0016] More specifically, the invention is a hydrocracking process thatcomprises the following stages:

[0017] A hydrorefining stage in which the feedstock is brought intocontact with at least one hydrorefining catalyst that exhibits in thestandard activity test a conversion rate of the methylcyclohexane thatis less than 10% by mass;

[0018] A hydrocracking stage in which at least a portion of the effluentthat is obtained from the hydrorefining stage is brought into contactwith at least one non-zeolitic hydrocracking catalyst that in thestandard activity test exhibits a conversion rate of themethylcyclohexane that is higher than 10% by mass.

[0019] First Reaction Zone

[0020] Very varied feedstocks can be treated by the process according tothe invention and generally they contain at least 20% by volume andoften at least 80% by volume of compounds that boil above 340° C.

[0021] The feedstock can form part of, for example, LCO (light cycleoil), atmospheric distillates, vacuum distillates, for example, gas oilthat is obtained from direct distillation of crude or conversion unitssuch as the FCC, the coker, or the visbreaking, as well as feedstocksthat are obtained from units for extracting aromatic compounds fromlubricating oil bases or obtained from solvent dewaxing of lubricatingoil bases, or else distillates that are obtained by desulfurization orhydroconversion of RAT (atmospheric residues) and/or RSV (vacuumresidues) or else the feedstock can be a desasphalted oil, or else anymixture of the feedstocks cited above. The list above is not limiting.The feedstocks preferably have a boiling point T5 that is higher than340° C., and better yet higher than 370° C., i.e., that 95% of thecompounds that are present in the feedstock have a boiling point that ishigher than 340° C., and better yet higher than 370° C.

[0022] The nitrogen content of the hydrocarbon feedstocks that aretreated in the process according to the invention is usually higher than500 ppm and preferably between 500 and 5000 ppm by weight, morepreferably between 700 and 4000 ppm by weight and even more preferablybetween 1000 and 4000 ppm. Generally, the sulfur content is between 0.01and 5% by weight, more generally between 0.2 and 4%. These feedstocksexhibit very low olefin contents.

[0023] In the first reaction zone, the feedstock undergoes at least onehydrorefining cycle (hydrodesulfurization, hydrodenitration,hydrogenation of aromatic compounds).

[0024] Standard catalysts can be used that contain at least oneamorphous substrate and at least one hydro-dehydrogenating element(generally at least one non-noble element of groups VIB and VIII, andmost often at least one element of group VIB and at least one non-nobleelement of group VIII).

[0025] Very advantageously, in the hydrocracking process according tothe invention, the feedstock that is to be treated is brought intocontact in the presence of hydrogen with a hydrorefining catalyst thatcomprises at least one matrix, at least one hydro-dehydrogenatingelement that is selected from the group that is formed by the elementsof group VIB and the non-noble group VIII of the periodic table,optionally at least one promoter element that is deposited on thecatalyst and selected from the group that is formed by phosphorus, boronand silicon, optionally at least one element of group VIIA (chlorine,fluorine are preferred) and optionally at least one element of groupVIIB (manganese is preferred), and optionally at least one element ofgroup VB (niobium is preferred).

[0026] The hydrorefining catalysts that are used do not contain zeoliteand exhibit a low acidity that is measured by a standard activity test(TSA).

[0027] We will now define this test and specify what is meant by lowacidity.

[0028] The object of the standard activity test is to measure theactivity of catalysts (such as those of hydrorefining described above)in the conversion of methylcyclohexane under the following operatingconditions:

[0029] The catalyst is sulfurized in advance under a pressure of 60 bar,at 350° C. with a so-called reaction mixture that comprises 0.5% by massof aniline, 1.5% by mass of dimethyl disulfide and 98% by mass ofmethylcyclohexane, for 4 hours. Then, always under the same reactionflow by adding hydrogen, and under the following reaction conditions:pressure of 60 bar, volumetric flow rate VVh of 1 h⁻¹, H2/reactionmixture ratio (described above): 1000 Nl of hydrogen/l of liquidreaction mixture (Nl=normal liters), the temperature is graduallybrought to a reaction temperature of 380° C.

[0030] Under these operating conditions, a catalyst is considered asexhibiting a low acidity and can therefore be used in the first reactionzone if it leads to a conversion rate of methylcyclohexane that is lessthan 10% by mass and preferably less than 5%.

[0031] The conversion of the methylcyclohexane reagent is defined as thetransformation of the latter into isomerization products with 7 carbonatoms, such as, for example, the dimethylcyclopentanes, intoring-opening products and into cracking products. The conversion ofmethyl cyclohexane, as defined, therefore takes into account all of thedifferent products of methyl cyclohexane. Obtaining all of theseproducts requires the presence of a more or less strong acid function onthe catalyst.

[0032] The hydrorefining catalysts that are used generally contain lessthan 10% by weight, and preferably at most 5% by weight, of silica. Inaddition, this silica is preferably brought by doping. The siliconpromoter element is then primarily located on the matrix and can becharacterized by the Castaing microprobe or another method as describedlater with the hydrocracking catalyst.

[0033] The preferred catalysts do not contain silica.

[0034] This catalyst preferably contains boron and/or silicon and/orphosphorus as a promoter element. The contents of boron, silicon andphosphorus are then 0.1-20%, preferably 0.1-15%, even moreadvantageously 0.1-10%.

[0035] The matrices that can be used alone or in a mixture are by way ofnonlimiting example alumina, halogenated alumina, clays (selected, forexample, from among the natural clays such as kaolin, or bentonite),magnesia, titanium oxide, boron oxide, zirconia, aluminum phosphates,titanium phosphates, zirconium phosphates, carbon, and aluminates. It ispreferred to use matrices that contain alumina in all of these formsthat are known to one skilled in the art and even more preferablyaluminas, for example gamma-alumina.

[0036] The role of hydro-dehydrogenating function is preferably filledby at least one metal or metal compound from group VIII that isnon-noble and VIB, preferably selected from among molybdenum, tungsten,nickel and cobalt. This role is preferably ensured by the combination ofat least one element of group VIII (Ni, Co) with at least one element ofgroup VIB (Mo, W).

[0037] This catalyst can advantageously contain phosphorus; actually, itis known in the prior art that this compound provides two advantages tohydrorefining catalysts: a facility for preparation in particular duringthe impregnation of nickel and molybdenum solutions and a betterhydrogenation activity.

[0038] In a preferred catalyst, the total content by mass of metaloxides of groups VI and VIII is most often between 5 and 60% andpreferably between 7 and 50%, and the ratio by weight that is expressedin terms of metal oxide between group VIB metal (or metals) vs. groupVIII metal (or metals) is preferably between 20 and 1.25 and even morepreferably between 10 and 2. The content by mass of phosphorus oxideP₂O₅ will be less than 15% and preferably 10%.

[0039] Another preferred catalyst that contains boron and/or silicon(and preferably boron and silicon) generally contains in % by weightrelative to the total mass of the catalyst at least one metal that isselected from the following groups and with the following contents:

[0040] 3 to 40%, preferably 3 to 35%, and even more preferably 3 to 30%of at least one metal of group VIB and optionally

[0041] 0 to 30%, preferably 0 to 25%, and even more preferably 0 to 20%of at least one metal of group VIII,

[0042] whereby the catalyst also contains at least one substrate that isselected from the following groups with the following contents:

[0043] 0 to 99%, advantageously 0.1 to 99%, preferably 10 to 98%, andeven more preferably 15 to 95% of at least one amorphous or poorlycrystallized matrix,

[0044] whereby said catalyst is characterized in that it also contains

[0045] 0.1 to 20%, preferably 0.1 to 15% and even more preferably 0.1 to10% of boron and/or 0.1 to 15%, preferably 0.1 to less than 10% and evenmore preferably 0.1 to 5% by weight of silicon,

[0046] and optionally

[0047] 0 to 20%, preferably 0.1 to 15%, and even more preferably 0.1 to10% of phosphorus,

[0048] and optionally also

[0049] 0 to 20%, preferably 0.1 to 15%, and even more preferably 0.1 to10% of at least one element that is selected from the group VIIA,preferably fluorine.

[0050] In general, the formulas that have the following atomic ratiosare preferred:

[0051] a group VIII metal/group VIB metals atomic ratio of between 0 and1,

[0052] a B/group VIB metals atomic ratio of between 0.01 and 3,

[0053] an Si/group VIB metals atomic ratio of between 0.01 and 1.5,

[0054] a P/group VIB metals atomic ratio of between 0.01 and 1,

[0055] a group VIIA element/group VIB metals atomic ratio of between0.01 and 2.

[0056] The preferred catalysts are the NiMo and/or NiW catalysts onalumina, also the NiMo and/or NiW catalysts on alumina doped with atleast one element included in the group of atoms formed by phosphorus,boron, silicon and fluorine.

[0057] In general, the hydrorefining catalyst contains:

[0058] 5-40% by weight of at least one non-noble element of groups VIBand VIII (% oxide),

[0059] 0-20% of at least one promoter element that is selected fromamong phosphorus, boron, (% oxide), preferably between 0.1-10% and evenmore preferably between 0.1 and 5% by weight; 0 to less than 10% byweight of promoter silicon, preferably 0.1-5%; advantageously boronand/or silicon are present, and optionally phosphorus.

[0060] 0-20% of at least one element of group VIIB (manganese, forexample)

[0061] 0-20% of at least one element of group VIIA (fluorine, chlorine,for example)

[0062] 0-60% of at least one element of group VB (niobium, for example)

[0063] 0.1-95% of at least one matrix, and preferably alumina.

[0064] The catalysts that are described above are generally used toensure the hydrorefining that is also called hydrotreatment.

[0065] Prior to the injection of the feedstock, the catalysts that areused in the process according to this invention are preferably subjectedin advance to a sulfurization treatment that makes it possible totransform, at least in part, metallic radicals into sulfide before theyare brought into contact with the feedstock that is to be treated. Thistreatment of activation by sulfurization is well known to one skilled inthe art and can be carried out by any method that is already describedin the literature or in situ, i.e., in the reactor, or ex situ.

[0066] A standard sulfurization method that is well known to one skilledin the art consists in heating in the presence of hydrogen sulfide (pureor, for example, under a stream of a hydrogen/hydrogen sulfide mixture)to a temperature of between 150 and 800° C., preferably between 250 and600° C., generally in a flushed-bed reaction zone.

[0067] In the first reaction zone of the process, the feedstock isbrought into contact, in the presence of hydrogen, with at least onecatalyst as described above, at a temperature of between 330 and 450°C., preferably 360-420° C., under a pressure that is higher than 7.5,preferably higher than 8.2 MPa, preferably higher than 9.0 MPa, and evenmore preferably higher than 11.0 MPa and lower than 20 MPa, whereby thevolumetric flow rate is between 0.1 and 6 h⁻¹, preferably 0.2-3 h⁻¹, andthe amount of hydrogen that is introduced is such that the liter ofhydrogen/liter of hydrocarbon volumetric ratio is between 100 and 2000l/l. Under these conditions, the conversion into products boiling below340° C. (and even below 370° C.) is most often less than 30% by weight,usually less than 20% and even 15%. A conversion in this stage is notdesired.

[0068] In the first reaction zone of the process according to theinvention, a significant reduction of the content of organicnitrogen-containing and sulfur-containing compounds and of condensedpolycyclic aromatic hydrocarbons is obtained. Under these conditions, atleast a portion of the nitrogen-containing and sulfur-containing organicproducts of the feedstock are also transformed into H₂S and into NH₃.

[0069] The operating conditions under which this hydrorefining iscarried out are such that the organic nitrogen content of the feedstockthat is obtained from this hydrorefining and that is then admitted tothe hydrocracking catalyst bed is less than 200 ppm by weight andpreferably less than 100 ppm by weight and even more preferably lessthan 80 ppm by weight.

[0070] The effluent that is obtained from this first reaction zone is atleast in part, and preferably completely, introduced into the secondreaction zone of the process according to the invention. An intermediateseparation of the gases can be carried out.

[0071] Second Reaction Zone

[0072] The operating conditions that are used in the reactor or reactorsthat are located downstream from the first reaction zone of the processaccording to the invention are: a temperature that is higher than 200°C., often between 250-480° C., advantageously between 320 and 450° C.,preferably between 330 and 425° C., under a pressure of between 3 MPaand 20 MPa, preferably higher than 7.5, preferably higher than 8.2 MPa,preferably higher than 9.0 MPa, or else higher than 11.0 MPa and lessthan 20 MPa, whereby the volumetric flow rate is between 0.1 and 20 h⁻¹,and preferably 0.1-6 h⁻¹, preferably 0.2-3 h⁻¹, and the amount ofhydrogen that is introduced is such that the liter of hydrogen/liter ofhydrocarbon volumetric ratio is between 80 and 5000 l/l and most oftenbetween 100 and 2000 l/l. Under these conditions, the overall conversionof the process is generally at least 50% by weight and preferably atleast 60% when the objective is to obtain middle distillates.

[0073] The process according to the invention is very advantageouslyoperable within 3 ranges of pressure making it possible to obtaindifferent yields and different qualities of products.

[0074] It is thus possible to work at low total pressures, generally ofat most 7.0 MPa, or high pressures, generally of at least 11 MPa, orwithin the intermediate range of moderate pressures that are higher than7 MPa and less than 11 MPa, generally of between 8.2-11 MPa.

[0075] Thus, in an advantageous way, within the ranges of low pressuresand primarily within ranges of moderate pressures, higher conversionlevels are achieved than with single hydrocracking catalysts.

[0076] This increase (it is the same at high pressures) is obtained onlyfrom the conversion provided by hydrotreatment (which is actually fairlylow) but primarily from modification of the feedstock.

[0077] These operating conditions that are used in the second reactionzone of the process according to the invention make it possible toachieve conversions per pass into products that have boiling points ofless than 340° C. and, better, less than 370° C., greater than 30% byweight and even more preferably between 40 and 95% by weight.

[0078] The second reaction zone comprises at least one reactor thatcontains at least one amorphous catalyst bed of hydrocracking. Thehydrocracking catalysts that are used in the hydrocracking processes areall of the bifunctional type combining an acid function with ahydrogenating function. The acid function is provided by large-surfacesubstrates (generally 150 to 800 m².g⁻¹) that exhibit a superficialacidity, such as the halogenated aluminas (chlorinated or fluorinated inparticular), combinations of boron oxides and aluminum oxides,combinations of titanium oxide, silicon oxide and aluminum oxide,combinations of zirconium oxides, aluminum oxides and silicon oxides,amorphous silica-aluminas, halogenated silica-aluminas (chlorinated orfluorinated in particular). These oxides or combinations of amorphousoxides can be obtained by any of the synthesis methods that are known toone skilled in the art.

[0079] The hydrogenating function is provided either by one or moremetals of group VIII of the periodic table or by a combination of atleast one metal of group VIB of the periodic table and at least onemetal of group VIII.

[0080] Said catalyst comprises at least one amorphous acid function suchas a silica-alumina, and at least one hydro-dehydrogenating function,optionally at least one matrix. Optionally, it can also contain at leastone element that is selected from among boron, phosphorus and silicon,at least one element of group VIIA (chlorine, fluorine, for example), atleast one element of group VIIB (manganese, for example), and at leastone element of group VB (niobium, for example).

[0081] According to a preferred method according to the invention, thehydrorefining catalyst and the hydrocracking catalyst are placed inseparate reactors. In another method, they are placed in the samereactor but in separate beds, and the entire hydrotreated effluent moveson to hydrocracking.

[0082] In all of the cases, the reactor or reactors that contain thehydrorefining catalyst is (are) upstream from the reactor or reactorscontaining the hydrocracking catalyst. In other words, the hydrocrackingcatalyst comes from a hydrorefining catalyst with a lower acidity thanthe hydrocracking catalyst.

[0083] Amorphous Catalyst

[0084] The non-zeolitic hydrocracking catalyst contains an amorphousacid function, generally a silica-alumina. It also contains ahydro-dehydrogenating function and optionally a matrix. It can alsooptionally contain at least one promoter element (boron, phosphorusand/or silicon); their content is generally 0-20%, preferably at least0.1%, advantageously 0.1-15% or else 0.1-10% or 0.1-5%. It optionallycontains at least one element of group VIIA (chlorine, fluorine) whosecontent is generally 0-20%, preferably at least 0.1%, advantageously0.1-15% or else 0.1-10%; fluorine is preferred. It can also contain atleast one element of group VIIB (manganese, for example), and at leastone element of group VB (niobium, for example). The element content ofgroup VIIB is 0-20%, preferably at least 0.1%. The element content byweight of group VB is 0-60%, preferably at least 0.1%.

[0085] The content by weight of silica of said silica-alumina is between10 and 95% and preferably between 20 and 90% and even more preferablybetween 30 and 90%. These silica-aluminas can be prepared by any of themethods that are known to one skilled in the art such as, for example,the methods of cogelation, coprecipitation, . . ..

[0086] The amorphous acid function can also be ensured by ternarymixtures of oxides such as titanium silica-alumina-oxide compositions orelse zirconia silica-alumina-oxide compositions. The silica-aluminasubstrates, or titanium silica-alumina-oxide substrates or else zirconiasilica-alumina-oxide substrates are prepared by all of the methods thatare known to one skilled in the art such as the methods of cogelation,coprecipitation, . . ..

[0087] The content by weight of silica of said ternary oxides is between10 and 90% and preferably between 20 and 90% and even more preferablybetween 30 and 85%. These ternary oxides can be prepared by any of themethods that are known to one skilled in the art, such as, for example,the methods of cogelation, coprecipitation, . . ..

[0088] The role of hydro-dehydrogenating function for the hydrocrackingcatalyst that comprises at least one acid function, as defined above, ispreferably filled by at least one non-noble metal or metal compound ofgroup VIII and of group VIB preferably selected from among molybdenum,tungsten, nickel and cobalt. This role is preferably ensured by thecombination of at least one element of group VIII (Ni) with at least oneelement of group VIB (Mo, W), whereby the total content by weight ofsaid metals is generally 5-40%.

[0089] Advantageous amorphous catalysts for hydrocracking are the NiMoand/or NiW catalysts on silica-alumina or on titaniumsilica-alumina-oxide or else on zirconia silica-alumina-oxide. Thesecatalysts can be prepared by any of the methods that are known to oneskilled in the art.

[0090] The catalysts that are described above and that are used in thesecond reaction zone are characterized in that they do not containzeolite and exhibit a higher acidity than that of catalysts that areused in the first reaction zone upstream. Their acidity is measured bythe standard activity test (TSA) that is described above.

[0091] Under these operating conditions, a catalyst is considered asexhibiting a sufficient acidity to be used in the second reaction zoneif it results in a methylcyclohexane conversion rate that is higher than10% by mass and preferably higher than 15%.

[0092] The substrate on which the metals are deposited can consist ofsilica-aluminas or ternary oxides as defined in the paragraphs above orresult from mixing said silica-aluminas or ternary oxides with a bindersuch as alumina (Al₂O), clays, and any mixture of binders cited above.The preferred binder is alumina and even more preferably alumina in allof these forms that are known to one skilled in the art, for examplegamma-alumina. The content by weight of binder in the catalyst is suchthat it makes it possible to obtain a level of acidity as described inthe standard activity test (TSA) in the preceding paragraph. Thesubstrate, defined as the mixing of a binder and at least one acidfunction that is selected from the group that is formed by thesilica-aluminas, the ternary oxides such as the titanium silixa-aluminaoxides and the zirconia silica-alumina-oxides, most often comprises acontent by weight of silica of at least 10% and preferably higher than20% and less than 95%, or, better, 90%.

[0093] The catalysts whose substrate consists only of silica alumina orternary oxides without any binder are preferred, however; they contain10-95% by weight of silica.

[0094] The substrate can be prepared by shaping silica-alumina orternary oxides with or without a binder by any technique that is knownto one skilled in the art. The shaping can be carried out by, forexample, extrusion, pelletizing, the drop (oil-drop) coagulation method,turntable granulation or by any other method that is well known to oneskilled in the art. At least one calcination can be carried out afterany of the stages of the preparation; it is usually carried out in airat a temperature of at least 150° C., preferably at least 300° C.

[0095] The catalysts that comprise at least one silica-alumina or aternary oxide as described above in the patent, a hydrogenating functionthat is generally ensured preferably by at least one metal that isselected from the group that is formed by the metals of group VIB andgroup VIII of the periodic table, also preferably comprise at least oneelement that is selected from the group that is formed by boron, siliconand phosphorus. The catalyst optionally contains at least one element ofgroup VIIA, preferably chlorine and fluorine, and also optionally atleast one element of group VIIB.

[0096] Boron, silicon, and/or phosphorus are preferably located onsilica-alumina, ternary oxide and/or the substrate in the case where abinder was used for shaping the silica-alumina or ternary oxide used.

[0097] The promoter element that is introduced, and in particularsilicon, is primarily located on the silica-alumina and/or the substrateand can be characterized by techniques such as the Castaing microprobe(distribution profile of various elements), transmission electronmicroscopy combined with an X analysis of the components of catalysts,or else by combining distribution mapping of the elements that arepresent in the catalyst by electronic microprobe.

[0098] The metals of group VIB and group VIII of the catalyst of thisinvention can be present completely or partially in metallic form and/oroxide form and/or sulfide form.

[0099] In the case where the acid phase is an amorphous silica-alumina,a usable catalyst, for example, comprises at least onehydro-dehydrogenating element (preferably deposited on the substrate)and a substrate that comprises (or preferably consists of) at least onesilica-alumina, whereby said silica-alumina has the followingcharacteristics:

[0100] A content by weight of silica SiO₂ of between 10 and 60%,preferably between 20 and 60% and even more preferably between 30 and50% by weight,

[0101] An Na content that is less than 300 ppm by weight and preferablyless than 200 ppm by weight,

[0102] A total pore volume of between 0.5 and 1.2 ml/g that is measuredby mercury porosimetry,

[0103] Whereby the porosity of said silica-alumina is as follows:

[0104] i/ The volume of mesopores whose diameter is between 40 Å and 150Å, and whose mean diameter varies between 80 and 120 Å representsbetween 30 and 80% of the total pore volume defined above and preferablybetween 40 and 70%.

[0105] ii/ The volume of macropores, whose diameter is larger than 500Å, and preferably between 1000 Å and 10,000 Å, represents between 20 and80% of the total pore volume and preferably between 30 and 60% of thetotal pore volume, and even more preferably the volume of the macroporesrepresents at least 35% of the total pore volume.

[0106] A specific surface area that is larger than 200 m²/g andpreferably larger than 250 m²/g.

[0107] In the case where the catalyst above is used in hydrocracking, acatalyst for hydrotreatment that contains Ni, Mo and P and alumina, orNi, Mo, phosphorus, alumina and silicon will be preferred; whereby thelatter will be brought as a dopant.

[0108] Prior to the injection of the hydrocarbon effluent in the secondreaction zone of the process according to this invention, the catalystis subjected to a sulfurization treatment that makes it possible totransform, at least in part, the metallic radicals into sulfide beforethey are brought into contact with the feedstock that is to be treated.This treatment of activation by sulfurization is well known to oneskilled in the art and can be carried out by any method that is alreadydescribed in the literature or in situ, i.e., in the reactor, or exsitu.

[0109] A standard sulfurization method that is well known to one skilledin the art consists in heating in the presence of hydrogen sulfide (pureor, for example, under a stream of a hydrogen/hydrogen sulfide mixture),to a temperature of between 150 and 800° C., preferably between 250 and600° C., generally in a flushed-bed reaction zone.

[0110] The proportion of catalytic volume of the catalyst with lowacidity that is present in the first reaction zone represents, accordingto the cases of 10 to 60% of total catalytic volume, preferably between15 and 50% and even more preferably between 20 and 45% of the totalcatalytic volume.

[0111] Final Separation

[0112] The effluent at the outlet of the second reaction zone of thehydrocracking process according to the invention is subjected to aso-called final separation (for example by atmospheric distillationoptionally followed by a vacuum distillation) so as to separate thegases (such as ammonia (NH₃) and hydrogen sulfide (H₂S), as well as theother light gases that are present, hydrogen and conversion products. .. ). At least one residual liquid fraction that essentially containsproducts whose boiling point is generally higher than 340° C. and thatcan be at least in part recycled upstream from the second reaction zoneof the process according to the invention, and preferably upstream fromthe hydrocracking catalyst that is based on silica-alumina is obtainedin a facility for production of middle distillates.

[0113] The conversion into products that have boiling points of lessthan 340° C. or else less than 370° C. is at least 50% by weight.

[0114] The following examples illustrate the invention without, however,limiting its scope.

EXAMPLE 1 Preparation of Catalysts

[0115] Hydrorefining catalyst C1 is obtained by dry impregnation of asubstrate A that consists of cubic gamma-alumina, in the form ofcylindrical extrudates with a diameter of 1.6 mm and that have a surfacearea of 250 m2/g, a pore volume that is measured with mercury of 0.60ml/g, by an aqueous solution that contains nickel salts, molybdenumsalts and phosphoric acid. The nickel salt is nickel nitrateNi(NO₃)₂.6H₂O and that of molybdenum is ammonium heptamolybdate(NH₄)₆Mo₇O₂₄.4H₂O.

[0116] After maturation at ambient temperature in a water-saturatedatmosphere, the impregnated extrudates are dried at 120° C. and thencalcined at 500° C. in dry air. The final content of MoO₃ is 17.1%, andthat of NiO is 3.7% by mass and that of P₂O₅ is 4.1% by mass.

[0117] Substrate B is a silica-alumina that has a chemical compositionof 40% by weight of SiO₂ and 60% by weight of Al₂O₃. Its Si/Al molarratio is 0.56. Its Na content is on the order of 100-120 ppm by weight.It is in the form of cylindrical extrudates with a diameter of 1.7 mm.Its specific surface area is 320 m²/g. Its total pore volume, measuredby mercury porosimetry, is 0.83 cc/g. The pore distribution is bimodal.In the domain of mesopores, we observe a broad peak of between 40 and150 Å with a dV/dD maximum toward 70 Å. On the substrate, macroporesthat have a size of greater than 500 Å represent about 40% of the totalpore volume.

[0118] Catalyst C2 is obtained by dry impregnation of substrate B by anaqueous solution that contains tungsten and nickel salts. The tungstensalt is ammonium metatungstate (NH₄)₆H₂W₁₂O₄₀*4H₂O and that of nickel isnickel nitrate Ni(NO₃)₂*6H₂O. After maturation at ambient temperature ina water-saturated atmosphere, the impregnated extrudates are dried at120° C. for one night and then calcined at 500° C. in dry air. The finalcontent of WO₃ is 25% by weight. The final content of NiO is 3.5% byweight.

EXAMPLE 2 Standard Activity Test (TSA) on Catalysts C1 and C2

[0119] Catalysts C1 and C2 are subjected to a standard activity test(TSA) as follows. The sulfurization stage of the catalysts is carriedout at a pressure of 60 bar, at 350° C. with a mixture that comprises0.5% by mass of aniline, 1.5% by mass of dimethyl disulfide and 98% bymass of methylcyclohexane, for 4 hours.

[0120] The catalyst is sulfurized in a fixed-bed reactor at a pressureof 60 bar, at 350° C. by means of a mixture that comprises 0.5% by massof aniline, 1.5% by mass of dimethyl disulfide, and 98% by mass ofmethylcyclohexane for 4 hours. Then, still in the same reaction streamand under the following operating conditions: pressure of 60 bar,volumetric flow rate VVh of 1 h⁻¹, H2/reaction mixture ratio (describedabove): 1000 Nl of hydrogen/l of liquid reaction mixture (Nl=normalliters), the temperature is brought gradually to 380° C.

[0121] Under these conditions, catalyst C1 leads to a conversion ofmethylcyclohexane of 6% by weight. It is therefore, as defined above inthe text, a catalyst that exhibits a low acidity.

[0122] Under the same operating conditions, catalyst C2 leads to aconversion of methylcyclohexane of 18% by weight. It therefore exhibitsan acidity that is higher than that of C2.

[0123] The conversion of the methylcyclohexane reagent is defined as thetransformation of the latter into isomerization products with 7 carbonatoms, such as, for example, the dimethylcyclopentanes, intoring-opening products and into cracking products. The conversion ofmethylcyclohexane, as defined, therefore takes into account all of thedifferent products of the methylcyclohexane. Obtaining all of theseproducts requires the presence of a more or less strong acid function onthe catalyst.

EXAMPLE 3 Use According to the Invention

[0124] The catalysts whose preparations are described in Example 1 areused to carry out the hydrocracking of a vacuum distillate whose maincharacteristics are provided below: Type of feedstock Vacuum distillateDensity at 15° C. 0.941 Sulfur, % by weight 2.9 Nitrogen, ppm by weight1400 Simulated Distillation DS: 0.5% p° C. 399 DS: 10% p° C. 422 DS: 50%p° C. 494 DS: 90% p° C. 566 DS: Final point ° C. 619

[0125] In the case of use according to the process of the invention byusing a pilot unit that comprises two flow-through fixed-bed reactors,the fluids circulate from bottom to top (up-flow). In the first reactor(upstream) is placed hydrorefining catalyst C1 that is described inExample 1, and in the second reactor (downstream) is placed theamorphous hydrocracking catalyst C2 that is also described in Example 1.The volume of catalyst C1 represents ⅓ of the total catalytic volume(C1+C2) and the volume of catalyst C2 represents the ⅔ remaining.

[0126] The sulfurization of the catalyst is carried out at 120 bar andat 350° C. by means of a direct distillation gas oil diluted with 2% byweight of DMDS.

[0127] After sulfurization, the catalytic test is carried out under thefollowing conditions: Total pressure  14 MPa T = 400° C. Overall VVH 0.7h⁻¹

[0128] The volumetric flow rate (VVh) is expressed relative to theentire catalytic volume (catalysts C1+C2).

[0129] The catalytic performance levels are expressed by the netconversion of products that have a boiling point of less than 370° C.,by the net selectivity of a middle distillate fraction of 150-370° C.,and the ratio of gas oil yield/kerosene yield in the middle distillatefraction. They are expressed from the results of simultaneousdistillation.

[0130] Net conversion CN is assumed to be equal to:

CN 370° C.=[(% of 370° C.⁻ _(effluents))−(% of 370° C.⁻_(feedstock))/[100−(% of 370° C._(feedstock))]

[0131] The net selectivity of middle distillate SN is assumed to beequal to:

SN definition=[(fraction of 150-370_(effluents))=(fraction of150-370_(fedstock))/[(% of 370° C._(effluents))−(% of 370° C.⁻_(feedstock))]

[0132] The gas oil yield/kerosene yield (go./ker.ratio) in the middledistillate fraction is assumed to be equal to:

Go./ker.ratio=yield of the fraction (250° C.-370° C.) of theeffluent/yield of the fraction (150° C.-250° C.) in the effluent.

[0133] The catalytic performance levels that are obtained are providedin Table 1 below.

EXAMPLE 4 Use Not in Accordance with the Invention

[0134] In this example, the amorphous hydrocracking catalyst C2 is notused according to the invention. In this case, catalyst C2 is used byitself. The sulfurization of the catalyst is carried out at 120 bars, at350° C. with a direct distillation gas oil that is diluted with 2% byweight of DMDS.

[0135] After sulfurization, the catalytic test is carried out under thefollowing conditions: Total pressure  14 MPa T = 400° C. Overall VVH 0.7h⁻¹

[0136] The volumetric flow rate (VVh) is expressed relative to thecatalytic volume of catalyst C2.

[0137] The definitions of conversions, selectivities and go./ker.ratioare equivalent to those that are described in Example 3.

[0138] The catalytic performance levels that are thus obtained areprovided in the tables below. TABLE 1 Catalytic Results CN 370° C.Catalyst VVh (h⁻¹) T° C. % by weight C1 + C2 0.7 400 59 C2 0.7 400 50

[0139] TABLE 2 Catalytic Results SN % by weight Middle Go./Ker. Ratio CN370° C. Distillate % by weight/% Catalyst VVh (h⁻¹) % by weight (DM) byweight C1 + C2 0.7 59 74 1.35 C2 0.7 59 70 1.28

[0140] The results that are noted in Table 1 demonstrate that, for thesame volumetric flow rate, amorphous hydrocracking catalyst C2 leads toa higher net conversion at iso temperature when it is used according tothe process of the invention, i.e., with a catalyst C1 with low acidityupstream, than when it is used by itself.

[0141] The results of Table 2 are obtained at the same volumetric flowrate, and the reaction temperature was adjusted to obtain the same netconversion in the cases.

[0142] The results that are noted in Table 2 demonstrate that for thesame volumetric flow rate and the same net conversion, amorphoushydrocracking catalyst C2 leads to a higher DM selectivity and a highergo./ker.ratio, when it is used according to the process of theinvention, i.e., with a catalyst C1 with low acidity upstream, than whenit is used by itself.

[0143] In other words, relative to a process that uses a volume V1 of ahydrocracking catalyst that is not preceded by a hydrotreatment, theupstream installation of hydrocracking of a volume V2 of ahydrotreatment catalyst makes it possible to increase the overallconversion and selectivity of the process while offering the possibilityof reducing the volume of hydrocracking catalyst, which is often themost expensive catalyst.

[0144] Without further elaboration, it is believed that one skilled inthe art can, using the preceding description, utilize the presentinvention to its fullest extent. The preceding preferred specificembodiments are, therefore, to be construed as merely illustrative, andnot limitative of the remainder of the disclosure in any way whatsoever.

[0145] In the foregoing and in the examples, all temperatures are setforth uncorrected in degrees Celsius, and all parts and percentages areby weight, unless otherwise indicated.

[0146] The entire disclosure of all applications, patents andpublications, cited herein and of corresponding French Application No.02/07,046, filed on Jun. 6, 2002, is incorporated by reference herein.

[0147] The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

[0148] From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting form the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. Process for hydrocracking that comprises the following successivestages: A hydrorefining stage in which the feedstock is brought intocontact with at least one hydrorefining catalyst that exhibits in thestandard activity test a conversion rate of the methylcyclohexane thatis less than 10% by mass; A hydrocracking stage in which at least aportion of the effluent that is obtained from the hydrocracking stage isbrought into contact with at least one non-zeolitic hydrocrackingcatalyst that in the standard activity test exhibits a conversion rateof methylcyclohexane that is higher than 10% by mass:
 2. Processaccording to claim 1, in which the hydrocracking catalyst contains10-95% by weight of silica.
 3. Process according to one of the precedingclaims, in which the hydrocracking catalyst comprises a substrate thatis selected from the group that is formed by the silica-aluminas, thetitanium silica-alumina-oxide compositions, the zirconiasilica-alumina-oxide compositions, and their mixtures with a binder. 4.Process according to one of the preceding claims, in which thehydrocracking catalyst comprises: 0-20% by weight of at least onepromoter element that is selected from the group that is formed byboron, phosphorus and silicon; 0-20% by weight of at least one elementof group VIIA; 0-20% by weight of at least one element of group VIIB;0-60% by weight of at least one element of group VB; 5-40% by weight ofat least one metal of group VIB and at least one metal of group VIIIthat is not noble (expressed in oxide).
 5. Process according to one ofthe preceding claims, in which all of the effluent that is obtained fromthe hydrorefining zone is sent into the hydrocracking zone.
 6. Processaccording to one of the preceding claims, in which the proportion of thehydrorefining catalytic volume represents 10-60% of the total catalyticvolume.
 7. Process according to one of the preceding claims in which thehydrotreatment catalyst does not contain silica.
 8. Process according toone of claims 1 to 6, in which the hydrotreatment catalyst containssilicon as a promoter element that is deposited on the matrix, wherebyits silica content is less than 10% by weight.
 9. Process according toone of the preceding claims, in which the feedstock contains at least20% by volume of compounds that boil above 340° C.; it exhibits anitrogen content that is higher than 500 ppm and a sulfur content ofbetween 0.01 and 5% by weight.